In our prior U.S. Pat. No. 3,844,745 we have disclosed a gas-purification system of this type comprising a main scrubbing station and a secondary scrubbing station in which gases to be purified are subjected to irrigation, the main scrubbing station receiving waste gases from an operating converter via a first duct whereas a second duct (or set of ducts) delivers waste gases from ancillary equipment to the secondary scrubbing station. A third duct, with an inlet positioned in the vicinity of the converter mouth, intercepts gases evolving during the charging thereof and directs them to the main scrubbing station which at that time is not utilized for the treatment of the converter gases themselves; this latter duct is selectively connectable, with the aid of a switching valve, to the secondary scrubbing station whereby airborne solids not exhausted by the first duct during a refining operation are extracted by the then not otherwise utilized (or underutilized) facility serving for the treatment of gases emitted by the ancillary equipment. Each duct is provided with individual irrigation means, including an upstream washing stage and a downstream washing stage in the first scrubbing station. The gases traversing the two scrubbing stations are subjected to the action of the respective irrigation means which are connected to a common source of wash water, such as a settling tank to which the effluents of both stations are led for recirculation of the liquid. This wash water is circulated in tandem through the two scrubbing stations, the effluent of the secondary station with its relatively minor load of contaminants being passed into the upstream washing stage in the main station whose downstream stage is supplied with fresh wash water directly from the source, as is a further washing stage located in the third duct. The first and third ducts merge within the main station downstream of their respective washing stages at the entrance of a common water separator.